Both high-speed and high-density data transmission channels are a request of modern and next-generation supercomputing and networking systems. Implementation of electrical wiring technologies for such channels requires overcoming a number of difficulties such as impedance matching problems, crosstalk effects, unwanted resonances, and so on.
Vertical interconnections connecting planar transmission lines disposed at different conductor layers are important elements to develop multilayer substrate technologies which are a cost-effective approach to dispose electrical wiring of high-speed systems. Therefore, improvement of impedance control and increase of density in the vertical interconnections satisfying simultaneously crosstalk requirements are complicated issues on a way in promotion higher speed in the systems.
There is a need for providing a multilayer substrate providing high-density vertical interconnections with improved impedance matching and reduced crosstalk effects between vertical interconnections.
Japanese Laid Open Patent Application No. JP-P2003-31945A discloses a multilayer substrate in which a number of vias are disposed within a clearance region. In such via configurations, however, a large crosstalk effect can be excited.
Japanese Laid Open Patent Application No. JP-A-Heisei, 06-85099 discloses that a via structure is shielded by ground vias connected with a ground strip at conductor layers. However, in high-density configurations, such shielding structure can not be applied between signal vias due to dimensional tolerances of a via fabrications process. Also, a real multilayer substrate consists of a number of different planar conductor layers such as analog and digital ground planes and power supply planes. At these layers, the strip cannot be connected to the ground vias due to the difference in the potential.
Japanese Laid Open Patent Application No. JP-P2005-277028A discloses that a ground strip is used to reduce crosstalk between signal via structures. In this case, however, it is also difficult to use such approach in high-density configurations.